Sterilization and celibacy

I hope you dont dismiss concerns/ questions. I am an asexual. I never wanted children. I lived 47 years withoug having a second thought, and never having changed my mind. I would have wanted to be sterilized so that there is no chance of pregnancy but I did not have opportunity and I always knew others would tell me to wait because I will change my mind, all that nonsense. I confess that the thought of surgery always made me uneasy but I have reasons of my own which currently are stronger than ever for wanting sterilization. I commonly participate as a paid research volunteer for money.I am going to assume that you are generally familiar with that. Mostly, sterilized females have the greatest chance to be picked for high paying studies. I would like info and advice on how I may arrange sterilization. I need to know if I would have to prove that I am sane like people who want sex change opertions. I dont have much room to write more. I will contact you in the future. Thank you